Manufacture of slag cement.



UNITED s PATENT orrrcn.

JOHN GUS'IAF ADOLIE RHODIN, OF LONDON, ENGLAND.

MANUFACTURE OF SLAG- CEMENT.

No Drawing.

It is well known that blast furnace slag may be transformed in various ways to produce a substance similar to Portlandcement.

The present process relates to a treatment of slag at a moderate temperature, viz.- 900 C. approximately, to produce cement. molten slag be granulated in connection with this invention no production of any effect is attempted on the molten slag itself, the operations under the present'invention beginning when the slag has cooled to the above mentioned temperature.

The essence of the present invention is a chemical treatment independent of any special form of apparatus. Any means of finely dividing slag and of keeping it at the above mentioned temperature during the herein described treatment will suit my purpose. I have discovered that it is possible to have a silicate react vigorously with lime and common salt at this temperature without the slightest sign of fusion, and that considerable quantitles of lime will enter into chemical combination with the silicate under these conditions.

One of the objects of thepresent invention is to chemically combine lime with blast furnace slag without sintering or fusion. Several other effects are, however, necessary in order to produce a completely sat-isfae tory cement from blast furnace slag. No process described so far. inthe art,-except actual clinkering with lime to Portland cement, has been quite satisfactory, as one or more necessary operations or additions has always been omitted.

My invention relates to :1. The temperature, at which the action takes place. 2. The composition of the atmosphere in which the action takes place. 3. The incorporation of lime into chemical combination with slag without fusion, or sintering. 4. The use of a contact substance for facilitating object 3. 5. The use of the other contact substance for improving the hydraulic properties of the resulting cement. 6. The use of a third contact substance for Speciflcationof Letters Patent.

Application filed February 28, 1910. Serial No. 545,552.

Patented Feb. 20, 1912.

rendering. the initial setting of the cement a permanent quality, and to make the cement store without alteration. 7. The combination of these effects in one operation.

The most favorable temperature lies at about 900 C. Withregard to the atmosphere employed, it must be of such character as to remove the bulk of sulfur, oc-

curring as sulfids in the slag, in the form of sulfurous acid instead of leaving it behind as gypsum in the cement, which is the main effect of oxidation in air. For this purpose I use an atmosphere of air and steam in admixture. In many'known processes such an atmosphere occurs, but its adjustment for this specific purpose is. not described, and the arrangements are such as. to make the action more or less incom lete and unessential, and the eflect is neither'claimed nor indicated. In experiments to elucidate the magnitude of the sufur-removing action, I treated a slag, containing 2.53% of sulfur: (a) by oxidation in air in an open mufile; and also (6) by oxidation in a mlxed atmosphere of steam and air in the same mufile.

The resulting product from (a) contained 2.20% of sulfur, showing a nearly. complete a flame at the mufile door. Calcium sulfate is undesirable in a cement in large proportions on account of lts retarding influence upon the setting time. To elucidate. this, I

made two lots of cement according to my complete process: (a) in an atmosphere of air only, and also (6) in a mixed atmosphere of air and steam. Cement (a) set to 'British standard in two hours, but (6') set in less than 10 minutes. As it is absolutely necessary for harbor work to have a cement setting in 11- hour or less, and as no cement, containing a large percentage of calcium sulfate will do this, combustion in a mixed atmosphereof air and steam is very advantageous in my process.

When incorporating lime in chemical combination into silicates at roughly 900 C., I have found the alkaline chlorids or calcium chlorid to be the most effective contact substances or reaction accelerants. A small percentage, say from J. to 1% per cent.

of common salt, mixed with finely divided duced into a furnace, which may be rotary. blast furnace slag and lime, causes the slag The slag may come hot from a granulator or to combine chemically with surprisingly atomizer of any construction, or it may be large quantities of lime atthe low temperaproduced by finely subdividing already cold ture of 900 C. Simultaneously the slag beslag. Either before or after its introduc- 70 comes soluble in acid, but the hydraulic tion the fine slag is mixed intimately with properties still leave a great deal to be dethe following chemicals: (1) a suitable sired. To improve these qualities a sulfate quantity of finely divided lime, (2) a lime salt of the type of magnesium-sulfate .or incorporating and reaction accelerating subferrous sulfate may be used in connection stance-such as an alkaline chlorid or cal- 75 with the common salt; The quantity must ciumchlorid, (3) if necessary, a small quanbe less than 2.5 per cent. of the whole, as tity of sulfate of iron or one of the alkaline large additions make the cement unsound. earths, (4E) asuitable quantity of a substance But this addition while advantageous for yielding calcium alumiriate at 900 C. In

its designated purpose, without other measthe furnace, the charge is kept at a tem- 80 ures gives a cement which is unsatisfactory, perature of approximately 900 (1., while a e. g., it loses its cementing properties at an current of air and steam is passedover the alarming rate, in fact it ceases to be a cc I same continuously. When the evolution of ment in a very few days. The object of such sulfur dioxid ceases, the charge is taken out an addition in as far as the present invention and cooled. If necessary, it is then ground 35 is concerned is to increasethe speed of the to flour, when it forms a marketable cement. after hardening in water, and for this pur- Sometimes it may be found advantageous pose it is useful, but for certain purposes it to grind the charge preliminarily to form may be omitted. a flour, and then no further grinding will be To make the cement keep, T have found necessary. 90 an addition of aluminate of lime, or a mix- With regard to quantities of chemicals I ture yielding aluminate of lime absolutely have found that an ordinary white pig slag essential. Aluminium salts per se are not containing 43 1 per cent. of lime (CaO) quite good for a dry process of producing yielded a really high class cement when cement, as the only one which is commertreated at 900 C. 1n the following mix- 95 cially possible, viz., crude aluminium sul' ture:100 parts of slag, 22.5 parts of lime fate cannot be powdered alone to a satis- (CaO), 0.75 parts of common salt (NaCL), factory. fineness for admixture with fine ce- 0.75 parts of crystallized magnesium sulment materials. Tf this salt is chosen, howfate, 1.5 parts of commercial crude aluever, I may mix it with slaked lime in minium sulfate containing per cent. of

a suitable mill, whereby a perfectly dry water. The proportions will naturally be powder is produced, which contains the elevaried according to the composition of-the ments of calcium aluminate. I .may also slag and the above is given as an example take natural bauxite as a raw material to only. In this case practically the wholeof 40 be admixed with lime in a similar manner. the lime entered into chemical combination 195 With this addition to my mixture, and treatwith the rest of the mixture, the gaged cement at 900 C. in a mixed atmosphere'of ment showing even less sweating of lime air and steam, I have produced cement, than Portland cement under similar condikeeping its properties for a practically in-- tions. The soundness of the cement was so 45 definite period. Tensile tests with a weeks great that the Le Chatelier test failed to interval came out almost identical. The obgive any indication whatever. The setting ject of this invention is therefore to combine time could be varied from fast to mein a single 0 eration several chemical acdlumtand slow by varying the proportions whlch a ect the various properties of tion of steam in the atmosphere.

50 a blast furnace slag cement formed at about Having now described the process in de- 900 0. without fusion or sinteringso as to tail what I claim is make a high grade hydraulic cement, which 1. In the manufacture of slag cement, th will store well, and the properties of which improvement which comprises incorporating can be varied at will to suit various pursuitable quantities of finely divided lime in 55 poses in the manner specified above. The chemical composition with solid finely diprocess is specially adapted for treating so vided blast furnace slag at a temperature becalled steel pig slags, containing about 40 low that at which any substantial fusion or per cent. of lime, by effecting the chemical slnteringtakes place and at about 900 C. combination of extra lime at a low temperaby means of a suitable contact substance 60 ture, whereby a normal hydraulic increase such as salt. I

of strength with time is obtained without 2. ln the manufacture of slag cement, the resort having to be taken to theexpensive improvement which comprises causing the clinkering process. chemical combination of finely divided lime in operation I roceed as follows :-A cerwith solid finely divided blast furnace slag t5 tain quantity of ely divided slag is introat a'temperature of about 900 C. by means of a suitable contact substance, while simultaneously removing sulfur in a volatile'form from the blast furnace slag by providing a mixed atmosphere of steam and air.

3. In the manufacture of slag cement, the improvement which comprises causing the chemical combination of finely divided lime with solid finely divided blast furnace slag, at a temperature of about 900 C; by means of a suitable contact substance, While improving the hydraulic properties of the re sult-infg slag by simultaneously treating with a fine y divided sulfate salt.

4. In the manufacture of slag cement, the improvement which comprises causing the chemical combination of finely divided. lime with solid finely divided blast furnace slag at a temperature of about 900 C. by means of a suitable contact substance, improving the hydraulic properties of the resulting slag by simultaneously treating with a finely divided sulfate salt, and simultaneously removing sulfur in a volatile form "from the blast furnace slag by providing a mixed atmosphere of steam and air.

5. The improvement in the manufacture of slag cement, which comprises chemically combining quantities of finely divided lime with finely divided blast furna'ceslag at a temperature of 900 C. by means of a suitable contact substance, and at the same time rendering the hydraulic properties of the hydraulic cement permanent by the addition of a finely divided mixture which will yield calcium aluminate at approximately the herein stated temperature.

6. The improvement in the manufacture of slag cement, which compriseschemically combining quantities of finely divided lime with finely divided blast furnace slag at a temperature of 900 C. by means of a suitable contact substance, rendering the hydraulic properties of the hydraulic cement permanent by the addition of a finely divided mixture which will yield calcium aluminate at approximately the herein stated temperature, and simultaneously removing the sulfur in a volatile form from the blast furnace slag by providing a mixed atmosphere of steam and air, said ste s being carried out in a single treatment in afurnace.

7. In the manufacture of slag cement, the method which comprises lacing in a nace a mixture containing nely divided slag and finely divided lime, a lime-incorporating substance, such as a chlorid, sulfate of iron, and a substance capable of yielding calcium aluminate at a temperature of approxi mately 900 C., and keeping the charge at a temperature of approximately 900 0., and at the same time passing a current of air and steam continuously over the charge.

' 8. In the manufacture of slag cement, the method which comprises placing in a furnace a mixture containing finely divided .blast furnace slag, finely divided lime, a

fur-

In testimony whereof I have signed my name to this specification in the presence of two subscribing wlt-nesses.

JOHN GUSTAF ADOLF RHODIN.

Witnesses:

HERBERT D. JAMESON, RIPLEY WILSON. 

